The invention relates to a system for the continuous injection of fuel into the induction tube of a mixture-compressing, internal combustion engine provided with a fuel metering and distribution assembly. In operation, a fuel pump delivers fuel continuously via a pressure regulator to the fuel metering and distribution assembly which distributes metered-out fuel through variable throttle apertures to injection valves embodied as control valves. The movable valve member of these fuel injection valves which obturates the valve orifice is attached to a diaphragm. One side of the diaphragm is subjected in an opening direction to the fuel pressure downstream of the fuel metering and distribution assembly. The other side is subjected to a counterforce exerted by a spring in opposition to the fuel pressure. The spring force acts to close the fuel injection valve.
In a known fuel injection system of this type, such as is disclosed for example in German published application 1,212,789, the diaphragm which controls the movable valve member of the injection valve is loaded in the opening direction by the fuel pressure prevailing downstream of the fuel metering and distribution assembly and it is loaded in the closing direction firstly by the force of a valve closing spring embodied as a helical compression spring and also by a secondary fuel pressure whose level has a fixed relation to the fuel pressure level prevailing upstream of the fuel metering and distribution assembly. The relationship between these two pressure levels is such that the secondary pressure, together with the force of the valve closing spring, determines the fuel pressure experienced by the other side of the diaphragm, i.e., the pressure prevailing downstream of the fuel metering and distribution assembly. The magnitude of the pressure experienced by the other side of the diaphragm is equal to the fuel pressure prevailing upstream of the fuel metering and distribution assembly diminished by the pressure drop across the associated throttle aperture within the metering assembly. This pressure drop is to be kept as constant as possible.
Thus, the injection valves are expected to perform the function of control valves with the object of maintaining the pressure drop across the associated throttle aperture within the fuel metering and distribution assembly within very narrow and negligible tolerance limits determined by the rigidity of the valve closing spring. This is done to insure a linear relationship between the injected fuel quantity per injection valve and the flow cross-section of the throttle aperture associated with that particular injection valve, independently of the pressure drop across the injection valve orifice, which varies with the air pressure in the induction tube of the engine, and also independently of any fuel pressure fluctuations upstream of the fuel metering and distribution assembly.
It is a disadvantage of this known fuel injection system that it requires considerable expenditures for structural elements and for supplementary fuel lines which are required for delivering fuel to the control diaphragm attached to the movable valve closing member of the injection valve so as to apply a control pressure which stands in a fixed relation with respect to the fuel pressure prevailing upstream of the fuel metering and distribution assembly.